Silica uptake from nanoparticles and silica condensation state in different tissues of Phragmites australis

Silicon is described as beneficial for grasses by enhancing yield and fitness via a considerable contribution to pathogen, drought, and pest resistance. Silicic acid is the predominant form for uptake and transport within the plant and will precipitate in leaves. But it is unknown whether polymeric nanosilicon compounds in its synthetic form, with an increasing concentration in aquatic environments, can be suitable for plant nutrition. Therefore, we investigated the uptake, transport, and deposition of silicic acid/silica within plants using synthetic nanosilica. Our results show a significant difference in silicon (Si) content within the different tissues of Phragmites australis. The nanosilica had been dissolved prior to the uptake by plants. The chemical form of Si during uptake was not traceable. A significant enhancement in the condensation state of the silica was found from root to leaves especially from culm to leaf tips visible by the increasing content of Q(4)-groups in the NMR spectra. We conclude that synthetic nanosilica has the same quality as source for the beneficial element Si like natural silica. Since the condensation state is described to control silica solubility, we suggest that different condensation states within the plant may result in different remobilization of silicon during decomposition of the plant material.